Method for ceramization of aluminum alloy surface

ABSTRACT

The present invention provides a method for ceramization of an aluminum alloy surface, comprising the steps of: (1) providing a clean aluminum alloy surface; (2) pre-polishing; (3) etching; (4) polishing; and (5) performing ceramic oxidation. The advantages of the method are as follows: (1) good corrosion resistance, good elasticity and insulation; (2) the coating being similar to plastic, with enamel-like luster and attractive appearance; and (3) good adsorption capacity, capability of being dyed with different colors, and good decorative effect etc.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Chinese Patent Application No. 201810327696.7, entitled METHOD FOR CERAMIZATION OF ALUMINUM ALLOY SURFACE and filed on Apr. 12, 2018, which is incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates to a surface treatment method for an alloy, specifically to a method for ceramization of an aluminum alloy surface.

BACKGROUND OF THE INVENTION

The surface of an aluminum alloy hub is generally treated by coating, vacuum coating, electroplating, etc., which not only plays a role in surface protection but also plays a decorative role. The vacuum coating and coating process requires multiple times of long-time baking for multiple times of film formation, so the process and equipment are complicated and the cost is high. At present, electroplating and coating combined wheel processes for aluminum hubs adopt the method of first electroplating and then coating. The conventional electroplating process has many shortcomings: 1, a polishing process is needed before electroplating; 2, the entire product surface is an electroplating layer by first electroplating, and the electroplating cost and the polishing cost are relatively expensive, so the raw material cost and the processing cost are both higher; 3, multiple times of baking is required during coating, which may result in foaming of a low-zone coating and high rejection rate; 4, after the electroplating, the rim should be adhered with special tape paper and then coated, wherein the tape paper is very high in cost and should be manually removed after the coating; 5, since the entire product surface needs to be electroplated, a low zone phenomenon occurs, and the electroplating qualification rate is low; 6, the de-plating repair cost is high, and the entire product needs to be completely de-plated and then re-plated; and 7, the nickel pre-plating step takes a long time, which results in a longer total time of the entire electroplating process.

Aluminum alloy ceramic oxidation, also known as glaze imitation oxidation, is a method of finishing an aluminum alloy, and unlike the conventional electroplating process, it is actually derived from an acid anhydride or oxalic acid anodization method. The product appearance is similar to ceramic glaze, enamel or plastic. The product has good corrosion resistance and can be dyed to achieve a good decorative effect.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a method for ceramization of an aluminum alloy surface so as to overcome the above problems.

Unless otherwise stated, all “solutions” in the description and claims of the present invention are aqueous solutions, and the components other than the solutes are water.

A method for ceramization of an aluminum alloy surface, comprising the steps of: (1) providing a clean aluminum alloy surface; (2) pre-polishing: rinsing the aluminum alloy surface obtained in step 1 in concentrated nitric acid for 1-5 minutes, followed by washing, the concentrated nitric acid being 380-400 g/L; (3) etching: rinsing the aluminum alloy surface obtained in step 2 in an etching solution for 1-5 minutes, followed by washing, the etching solution containing 45-50 g/L of sodium hydroxide and 45-50 g/L of sodium fluoride, and the temperature being 60-70° C.; (4) polishing: rinsing the aluminum alloy surface obtained in step 3 in concentrated nitric acid for 1-5 minutes, followed by washing, the concentrated nitric acid being 380-400 g/L; and (5) performing ceramic oxidation: electroplating the aluminum alloy surface in a ceramic oxidation solution for 45-48 minutes, followed by washing, the aluminum alloy surface being an anode, the current density of the anode being 0.5-1.0 A/dm², the voltage being 28-38V and the temperature being 45-50° C., and the ceramic oxidation solution comprising 36-38 g/L of chromic anhydride and 6-11 g/L of oxalic acid.

In step 1, the clean aluminum alloy surface is obtained by the following method: (1A) rinsing with an alkaline solution without sodium hydroxide at 25-35° C. for 15-20 minutes, and (1B) hot water washing followed by cold water washing.

In step 2, the aluminum alloy surface obtained in step 1 is rinsed in concentrated nitric acid for 4 minutes, and then washed, the concentrated nitric acid being 390 g/L.

In step 3, the aluminum alloy surface obtained in step 2 is rinsed in an etching solution for 4 minutes, and then washed, the etching solution containing 47 g/L of sodium hydroxide and 47 g/L of sodium fluoride, and the temperature being 65° C.

After step 3, hot water washing is followed by cold water washing; the hot water washing is performed 1-5 minutes, and the water temperature is 60-80° C.; the cold water washing is performed 1-5 minutes, and the water temperature is 15-20° C.

In step 4, the aluminum alloy surface obtained in step 3 is rinsed in concentrated nitric acid for 4 minutes, and then washed, the concentrated nitric acid being 390 g/L.

The method for ceramization of an aluminum alloy surface, further comprising a step of rinsing the aluminum alloy surface under a high pressure water gun between steps 4 and 5, the water pressure of the high pressure water gun being 1200-1400 Bar and the rinsing time being 30-60 seconds.

The method for ceramization of an aluminum alloy surface a, in step 5, the aluminum alloy surface is electroplated in a ceramic oxidation solution for 46 minutes, and then washed and dyed, the aluminum alloy surface being an anode, the current density of the anode being 0.72 A/dm², the voltage being 32V and the temperature being 47° C.

The method for ceramization of an aluminum alloy surface, further comprising step 6 of dyeing the aluminum alloy surface obtained in step 5 with a dye after step 5.

The method for ceramization of an aluminum alloy surface, the step of dyeing is selected from the group consisting of: (6A) dyeing at 25-35° C. for 6-8 minutes using a blue dyeing solution containing 12-48 g/L of potassium ferrocyanide and 25-80 g/L of potassium chloride; (6B) dyeing at 20-25° C. for 6-8 minutes using a black dyeing solution containing 55-85 g/L of cobalt acetate and 20-25 g/L of potassium permanganate; and (6C) dyeing at 25-35° C. for 6-8 minutes using a white dyeing solution containing 10-50 g/L of lead acetate and 20-40 g/L of sodium sulfate.

The advantages of the method according to the present invention are as follows: (1) good corrosion resistance, good elasticity and insulation; (2) the coating being similar to plastic, with enamel-like luster and attractive appearance; and (3) good adsorption capacity, capability of being dyed with different colors, and good decorative effect.

DETAILED DESCRIPTION OF THE EMBODIMENTS Embodiment 1

1. Test Equipment

Heat, acid and alkali resistant plastic tank: 30 L; rectifier (oxidation power supply): 200A/100V.

Plate: lead and lead-bismuth alloy plates; poles and wires: copper bars, copper wires

Material: aluminum alloy hub.

2. Dosing

1. Chromic acid and boric acid method (prepare 30 L solution)

Weigh 1120 g (40 g/L) of industrial-grade chromic anhydride and 84 g (3 g/L) of industrial-grade boric acid, dissolve into distilled water respectively, then add into a 30 L tank, and add distilled water to a prescribed volume for later use. In this method, the current density during electroplating process is 0.5-1.0 A/dm².

2. Anodization and Anodization Post-Treatment

Heat with a heater, stir with compressed-air and hang anode plates bilaterally for oxidation under stable voltage, and fill with distilled water of about 90° C. for 30-60 minutes after anodization.

3. Process Test and Results

The method (FIG. 1) comprises the steps of: (1) providing a clean aluminum alloy surface, the clean aluminum alloy surface being obtained by the following method: (1A) rinsing with an alkaline solution without sodium hydroxide at 30° C. for 18 minutes, and (1B) hot water washing followed by cold water washing; (2) pre-polishing: rinsing the aluminum alloy surface obtained in step 1 in concentrated nitric acid for 4 minutes, followed by washing, the concentrated nitric acid being 390 g/L; (3) rinsing the aluminum alloy surface obtained in step 2 in an etching solution for 4 minutes, followed by washing, the etching solution containing 47 g/L of sodium hydroxide and 47 g/L of sodium fluoride, and the temperature being 65° C.; (4) polishing: rinsing the aluminum alloy surface obtained in step 3 in concentrated nitric acid for 4 minutes, followed by washing, the concentrated nitric acid being 390 g/L; and (5) performing ceramic oxidation: electroplating the aluminum alloy surface obtained in step 4 in a ceramic oxidation solution for 46 minutes, followed by washing and dyeing, the aluminum alloy surface being an anode, the current density of the anode being 0.72 A/dm², the voltage being 32V and the temperature being 47° C., and the ceramic oxidation solution comprising 37 g/L of chromic anhydride and 8 g/L of oxalic acid.

In this embodiment, the following three dyeing conditions are taken:

A: dyeing at 28° C for 7 minutes using a blue dyeing solution containing 30 g/L of potassium ferrocyanide and 40 g/L of potassium chloride.

B: dyeing at 28° C. for 7 minutes using a black dyeing solution containing 75 g/L of cobalt acetate and 22 g/L of potassium permanganate.

C: dyeing at 28° C. for 7 minutes using a white dyeing solution containing 30 g/L of lead acetate and 30 g/L of sodium sulfate.

4. Process Test Conclusion

After the test, the aluminum alloy ceramic anode oxidation film showed the following characteristics. The color of the aluminum alloy ceramic anode oxidation film is different due to different material states. The film is opaque and looks like enamel. The film is dense, and has high hardness, wear resistance, good heat insulation and electrical insulation. From the perspective of process operation, the chromic acid and boric acid method is stable, simple to operate and easy to grasp.

Embodiment 2

The method of this embodiment differs from Embodiment 1 in a step of rinsing the aluminum alloy surface under a high pressure water gun between steps 4 and 5, the water pressure of the high pressure water gun being 1360 Bar, and the rinsing time being 45 seconds.

In this embodiment, the following three dyeing conditions are taken:

A: dyeing at 28° C. for 7 minutes using a blue dyeing solution containing 30 g/L of potassium ferrocyanide and 40 g/L of potassium chloride.

B: dyeing at 28° C. for 7 minutes using a black dyeing solution containing 75 g/L of cobalt acetate and 22 g/L of potassium permanganate.

C: dyeing at 28° C. for 7 minutes using a white dyeing solution containing 30 g/L of lead acetate and 30 g/L of sodium sulfate.

Embodiment 3

In this embodiment, the six surfaces obtained in Embodiments 1 and 2 were subjected to a copper accelerated acetic acid spray test respectively. The test was carried out in accordance with the methods described in GMW 14458:2011 (General Motors Worldwide Copper-Accelerated Acetic Acid Salt Spray (CASS) Test) and GMW 14729:2012 (General Motors Worldwide High Humidity Test). The results of samples were evaluated after exposure for 250, 500, 1000, 1250 and 1500 hours, and the results were shown in Table 1. The experiment was carried out in (SF2000SF2000SF2000)7# salt spray test chamber salt, and the test was completed by the Test Center of CITIC Daika Co., Ltd.

It can be seen from Table 1 that all the surfaces passed the CASS test of 1250 hours after the high pressure rinsing step was introduced in Embodiment 2, and had better protection capability. 

The invention claimed is:
 1. A method for ceramization of an aluminum alloy surface, comprising the steps of: (1) providing a clean aluminum alloy surface; (2) pre-polishing: rinsing the aluminum alloy surface obtained in step 1 in concentrated nitric acid for 1-5 minutes, followed by washing, the concentrated nitric acid being 380-400 g/L; (3) etching: rinsing the aluminum alloy surface obtained in step 2 in an etching solution for 1-5 minutes, followed by washing, the etching solution containing 45-50 g/L of sodium hydroxide and 45-50 g/L of sodium fluoride, and the temperature being 60-70° C.; (4) polishing: rinsing the aluminum alloy surface obtained in step 3 in concentrated nitric acid for 1-5 minutes, followed by washing, the concentrated nitric acid being 380-400 g/L; and (5) performing ceramic oxidation: electroplating the aluminum alloy surface in a ceramic oxidation solution for 45-48 minutes, followed by washing, the aluminum alloy surface being an anode, a current density of the anode being 0.5-1.0 A/dm², a voltage being 28-38V and a temperature being 45-50° C., and the ceramic oxidation solution comprising 36-38 g/L of chromic anhydride and 6-11 g/L of oxalic acid.
 2. The method for ceramization of an aluminum alloy surface according to claim 1, wherein in step 1, the clean aluminum alloy surface is obtained by the following method: (1A) rinsing with an alkaline solution without sodium hydroxide at 25-35° C. for 15-20 minutes, and (1B) hot water washing followed by cold water washing.
 3. The method for ceramization of an aluminum alloy surface according to claim 1, wherein in step 2, the aluminum alloy surface obtained in step 1 is rinsed in concentrated nitric acid for 4 minutes, and then washed, the concentrated nitric acid is 390 g/L.
 4. The method for ceramization of an aluminum alloy surface according to claim 1, wherein in step 3, the aluminum alloy surface obtained in step 2 is rinsed in an etching solution for 4 minutes, and then washed, the etching solution contains 47 g/L of sodium hydroxide and 47 g/L of sodium fluoride, and the temperature is 65° C.
 5. The method for ceramization of an aluminum alloy surface according to claim 1, wherein after step 3, hot water washing is followed by cold water washing; the hot water washing is performed 1-5 minutes, and a water temperature is 60-80° C.; the cold water washing is performed 1-5 minutes, and a water temperature is 15-20° C.
 6. The method for ceramization of an aluminum alloy surface according to claim 1, wherein in step 4, the aluminum alloy surface obtained in step 3 is rinsed in concentrated nitric acid for 4 minutes, and then washed, the concentrated nitric acid is 390 g/L.
 7. The method for ceramization of an aluminum alloy surface according to claim 1, further comprising a step of rinsing the aluminum alloy surface under a high pressure water gun between steps 4 and 5, a water pressure of the high pressure water gun is 1200-1400 Bar and a rinsing time is 30-60 seconds.
 8. The method for ceramization of an aluminum alloy surface according to claim 1, wherein in step 5, the aluminum alloy surface is electroplated in a ceramic oxidation solution for 46 minutes, and then washed and dyed, the aluminum alloy surface is an anode, a current density of the anode is 0.72 A/dm², a voltage is 32V and a temperature is 47° C.
 9. The method for ceramization of an aluminum alloy surface according to claim 1, further comprising step 6 of dyeing the aluminum alloy surface obtained in step 5 with a dye after step
 5. 10. The method for ceramization of an aluminum alloy surface according to claim 9, wherein the step of dyeing is selected from the group consisting of: (6A) dyeing at 25-35° C. for 6-8 minutes using a blue dyeing solution containing 12-48 g/L of potassium ferrocyanide and 25-80 g/L of potassium chloride; (6B) dyeing at 20-25° C. for 6-8 minutes using a black dyeing solution containing 55-85 g/L of cobalt acetate and 20-25 g/L of potassium permanganate; and (6C) dyeing at 25-35° C. for 6-8 minutes using a white dyeing solution containing 10-50 g/L of lead acetate and 20-40 g/L of sodium sulfate. 